The present invention relates to a novel mechanism for automatically regulating tension of wires employed in a window regulator (hereinafter referred to as "mechanism"), and, more particularly, to a mechanism which is used in a driving device of the window regulator and which can automatically eliminate looseness or permanent elongation of wires.
Until now, a window regulator, in which flexible wires are employed as a power transmitting means, has been used in doors of a car, or the like. In such a window regulator, looseness due to backlash or play of various connecting portions in the window regulator occurs in the wires and further, a permanent elongation occurs in the wires in the course of operation. Also, looseness tends to remain in the wires after the window regulator is assembled.
Such looseness or permanent elongation of wires causes the following disadvantages: For example, a window glass shakes in the up-and-down directions due to vibration of a car, or the like; a crank lever shakes due to vibration of a car, or the like; the window glass is stained since greased wires come in touch with the window glass; and a whipping noise of wires is generated in the doors due to vibration of a car, or the like. Such disadvantages offend a driver, or the like. Further, loosed wires tend to come off from a guide member or a pulley for guiding wires, and tend to be damaged. Therefore, the window regulator becomes inoperable occasionally.
Therefore, hitherto there has been proposed various means for eliminating looseness or permanent elongation of wires in order to suitably regulate tension of wires.
For example, there has been a tension-regulating mechanism for extending the length of wire-path, by means of a spring urging an outer casing (conduit), capable of slidably guiding a wire, toward an associating member with which the outer casing is to associate at one end of the outer casing, or by means of a tension pulley. Further, Italian Patent No. 927,030 (corresponding to British Patent No. 1382330) discloses another mechanism which can eliminate looseness of wires by means of manually rotating a ratchet plate relatively to the drum. The ratchet plate is adjacent to a wire-winding drum having a ratchet teeth and engaging with an end of a wire.
However, as to the former mechanism, there is a problem that it is somewhat hard to operate the device, since the wire is always stretched strongly. As to the latter mechanism, there are some problems that it is practically impossible to regulate tension of wires after the mechanism is installed in an inside of a door of a car, or the like.
As a solution of those problems, U.S. Pat. No. 4,440,354 proposes mechanisms. In one mechanism, a winding drum is divided into a first pulley and a second pulley. Both pulleys are engaged with each other, are capable of rotating in the relative direction, and have ratchet teeth on the facing side surfaces respectively. One end of each wire is engaged with the first pulley and the second pulley, respectively. In another mechanism, a cavity, in which a spiral spring can be contained, is dug in the second pulley. However, the former mechanism has no function of balancing between force for raising the window glass and force for lowering the window glass, and no function of reducing the force for raising the window glass, since a spiral spring is not employed. As to the latter mechanism, in spite of having the spiral spring, the size of the spiral spring is restricted by the size (the diameter and the depth) of the cavity dug in the second pulley. Accordingly, the spiral spring is not substantially employed in the latter mechanism, except a spiral spring of which diameter and width are small, i.e. the urging force of the spiral spring is weak. Namely, the relative rotation of the first pulley and the second pulley is caused by a torque of a crank lever, by a braking force, i.e. a frictional resistance which is applied to the second pulley when the first pulley is rotated, and by the urging force of the spiral spring. However, the frictional resistance is not a suitable element, since the frictional resistance depends upon various conditions, i.e. roughness of each contacting surface, pressure between the pulleys, existence of some adhesion on the sliding portions, and the like. Also, the frictional resistance changes due to abrasion generated in the course of operation. Therefore, a dispersion of tension values becomes broad occasionally. Further, labor of the operation is large in case of rotating the second pulley since the frictional resistance is applied to the second pulley not only in one direction but also in the opposite direction.
In order to solve the above problems, it is desired that the spiral spring having high urging force as much as possible is employed. Namely, if the urging force of such spiral spring rotates the ratchet teeth in the direction of idling movement, tension can be regulated more precisely, and the operational labor can be decreased, as compared with the case of the above frictional resistance.
"Idling movement" or "move idly" described in the specification means that, when a torque due to the relative rotation of a first ratchet teeth and a second ratchet teeth by means of rotating a crank lever generates, slant portions of the first ratchet teeth and the second ratchet teeth slip in the rotational direction with each other, and both ratchet teeth move axially in the opposed direction with each other, and at last the ratchet teeth engage again. Further, the conception of "idling movement" or "move idly" includes not only a case that one ratchet teeth moves in the axial direction and rotates around the axis, but also various cases, e.g. the case that one ratchet teeth moves in the axial direction and the other ratchet teeth rotates around the axis, or the case that both of the ratchet teeth move axially so as to depart away with each other, and one or both ratchet teeth rotate around the axis in the opposite directions.
On the other hand, when the spiral spring is adapted to support weight of the window glass or to balance the force for raising the window glass with the force for lowering the window glass, the urging force for balancing is not sufficient, since the size of the spiral spring is restricted by the size of the cavity dug in the conventional second pulley. In this respect, it is desired that the urging force of the spiral spring is increased as much as possible. Particularly, it is desired that the diameter, in the state of setting, of the spiral spring is large as much as possible in order to thin the whole thickness of the mechanism.
However, it is desired to reduce the operational force of the crank lever by means of increasing a ratio of a length of the crank lever to the diameter of the second pulley, i.e. by means of decreasing the diameter of the pulley. In order to satisfy the contradictory demands at the same time, it is thinkable to take out the spiral spring from the cavity of the second pulley, and to locate at another portion. However, in that case, there happens a problem that the whole thickness of the driving device increases.